For example, PTC heaters which are one form of electric heaters have a structure in which heat is generated by energizing a PTC element which is a resistive element having a positive temperature coefficient by a DC power supply (for example, PTL 1). PTC heaters are widely used because a resistance thereof rapidly increases as temperature increases at a certain timing and thus a constant temperature can be maintained by simple energization from the DC power supply, leading to a simple control structure.